The whole city is criss-crossed by an intricate labyrinth of sewers and pipes made of all kinds of materials. Some are prefabricated from stoneware, concrete, cast iron, steel, plastic or fibreglass, and are laid in an excavated tunnel. Others are built on-site by specialist sewer masons using impermeable sewer bricks. These sewers usually have an ovoid cross section, which has good hydraulic properties and is better at withstanding the pressure from the soil above.
But there is far more to the sewer network than the sewers alone. Special shafts for access, ventilation, measurement and sewer flushing also have their parts to play. And then there are drop shafts and chutes to deal with gradients where water would exceed the maximum flow rate, pumping stations to overcome differences in height or drive out water during floods, culverts under railway tracks and roads, and inverted siphons under rivers. The network also includes a variety of flood protection structures, which in Prague are installed along the entire Vltava River section: stoplog chambers, overflow chambers and pipes, flood gates, mains sewer interconnectors, and a newly-built retention tank in Karlín.
As the city’s population and sanitation needs grew, city officials had to come up with a systemic solution for Prague’s sewer network and wastewater treatment. They therefore invited tenders for the design of a comprehensive plan for Prague’s sewer system, where the aim was a unified system for all parts of the city that would also allow surrounding districts to be connected later. After many different ideas had been put forward, they finally approached the English civil engineer William Heerlein Lindley.
He produced an integrated design for Prague’s drainage system that took account of floods and rainfall, and involved tunnelling through the cliffs under Letná so the entire sewer network could discharge at Císařský Island in the Bubeneč district, where a treatment plant was proposed. This network was then divided into two sub-systems, A and B. The first of these drained the parts of the city whose water flowed through the Letná hill tunnel, and the second collected wastewater from Karlín and Holešovice.
The system handled the growing population with ease, and even though kilometres of new pipes have since been added, the trunk sewers still have the capacity to carry sewage from the whole city, either to the Central Wastewater Treatment Plant in Bubeneč or to branch treatment plants.
... the “Foreign Visitors’ Entrance” under Prague’s Old Town Hall was built at the request of Emperor Franz Joseph I as a showpiece for Prague’s sewer system?
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